Abstract:

White mold, caused by Sclerotinia sclerotiorum (Lib.) De Bary, is a destructive yield-limiting disease of common bean (Phaseolus vulgaris L.). Genetic resistance to this pathogen is limited in common bean. Identification of high levels of partial physiological resistance in a genetically cross compatible species, Phaseolus coccineus, is advisable. The objectives of this study were to 1) identify accessions of P. coccineus with high levels of partial physiological resistance to S. sclerotiorum, 2) create a linkage map in a P. coccineus population and 3) identify markers linked to quantitative trait loci (QTL) conferring partial physiological resistance to white mold in this population.
The P. coccineus collection of the U.S. Department of Agriculture National Plant Germplasm System (NPGS) Plant Introduction collection maintained at Pullman, WA, consisting of 478 accessions, but only 364 were available to be screened with the pathogen S. sclerotiorum to identify partial physiological resistance. 50.1% of the accessions were identified to have high partial physiological resistance using the Petzoldt and Dickson (1996). Accessions were also characterized as to what species they were, based on hilum and seed coat appearance and emergence. Almost 30% of the accessions' seeds were either a mixture of species or labeled the wrong species.
A population of P. coccineus, based on the cross Wolven Pole (MS) x PI 255956 (R), segregating for resistance was developed and evaluated for its susceptibility to white mold in the greenhouse. This population was then tested with three polymerase chain reaction (PCR) based markers, random amplified polymorphic DNAs (RAPDs), simple sequence repeats (SSRs), and amplified fragment length polymorphisms (AFLPs). A total of 215 markers were used to create a genetic linkage map with thirteen linkage groups that spanned 797 centimorgans (cM). Four quantative trait loci (QTL) were identified and placed on this map. The two QTL relating to a five week white mold screening explained a total of 89.6% of the phenotypic variation for this trait. The remaining two QTL were for the eight-day straw test results, and were able to explain 13.8% of the phenotypic variation. To our knowledge this is the first genetic linkage map of P. coccineus.